Synthesis of a dilithiobutadiene bearing extremely bulky silyl substituents and its reactivity toward functionalized silanes.

The synthesis and full characterization of 1,4-dilithio-1,4-bis(triisopropylsilyl)-2,3-diphenylbuta-1,3-diene (1b) are reported. This molecule featuring extremely bulky silyl groups at the 1- and 4-positions serves as a precursor for the synthesis of 2,5-bis(triisopropylsilyl)-3,4-diphenyl-1-silacyclopenta-1,3-dienes (siloles) bearing various substituents at the silicon atom (SiR = SiH (4), SiH(OMe) (5), SiF (6), SiBr (7), SiBr(OMe) (8)). Importantly, compounds 6 and 7 reacted with lithium to afford 2,5-bis(triisopropylsilyl)-3,4-diphenyldilithiosilole (9).

Charge Transport through Single-Molecule Junctions with σ-Delocalized Systems.

Single-molecule junctions, formed by a single molecule bridging a gap between two metal electrodes, are attracting attention as basic models of ultrasmall electronic devices. Although charge transport through π-conjugated molecules with π-delocalized system has been widely studied for a number of molecular junctions, there has been almost no research on charge transport through molecular junctions with a σ-delocalized orbital system. Compounds with hexa-selenium-substituted benzene form a σ-delocalized orbital system on the periphery of the benzene ring.

Activating a [FeFe] Hydrogenase Mimic for Hydrogen Evolution under Visible Light.

Inspired by the active center of the natural [FeFe] hydrogenases, we designed a compact and precious metal-free photosensitizer-catalyst dyad (PS-CAT) for photocatalytic hydrogen evolution under visible light irradiation. PS-CAT represents a prototype dyad comprising π-conjugated oligothiophenes as light absorbers. PS-CAT and its interaction with the sacrificial donor 1,3-dimethyl-2-phenylbenzimidazoline were studied by steady-state and time-resolved spectroscopy coupled with electrochemical techniques and visible light-driven photocatalytic investigations.

Ferroelectric columnar assemblies from the bowl-to-bowl inversion of aromatic cores.

Organic ferroelectrics, in which the constituent molecules retain remanent polarization, represent an important topic in condensed-matter science, and their attractive properties, which include lightness, flexibility, and non-toxicity, are of potential use in state-of-the-art ferroelectric devices. However, the mechanisms for the generation of ferroelectricity in such organic compounds remain limited to a few representative concepts, which has hitherto severely hampered progress in this area. Here, we demonstrate that a bowl-to-bowl inversion of a relatively small organic molecule with a bowl-shaped π-aromatic core generates ferroelectric dipole relaxation.

C and Pb NMR Chemical Shifts of Dirhodio- and Dilithioplumbole Complexes: A Quantum Chemical Assessment.

Density functional theory (DFT) and zeroth-order regular approximation DFT calculations were performed to investigate the electronic structures and C and Pb nuclear magnetic resonance (NMR) chemical shifts of metal-coordinated plumboles, namely, monorhodioplumbole ([Rh-plumbole]), dirhodioplumbole (Rh-plumbole), and dilithioplumbole (Li-plumbole), which have a five-membered ring containing lead. The molecular orbital correlation diagram and extended transition state-natural orbitals for chemical valence analysis of the [Rh-plumbole] and Rh-plumbole complexes showed that the plumbole is primarily a π-donor, with π-donation being dominant in the Rh-plumbole complex. The present calculations show that the Pb-C internuclear distances are longer in the Rh-plumbole complex than in [Rh-plumbole] because of the combined effect of strong π-donation and weak π-back-donation in the Rh-plumbole complex.

Heterobimetallic triple-decker complexes derived from a dianionic aromatic stannole ligand.

A neutral heterobimetallic triple-decker stannole complex was prepared by the reaction of an anionic ruthenocene bearing a stannole dianionic ligand with [Rh(cod)Cl]2 (cod = 1,5-cyclooctadiene), and the resulting Ru-Rh complex exhibits an electronic property different from those of the corresponding Ru-Ru and Rh-Rh complexes. The Ru-Rh complex can be decomposed in ionic liquids to metal nanoparticles.

Transition-Metal Complexes Featuring Dianionic Heavy Group 14 Element Aromatic Ligands.

The synthesis of dilithio-stannoles and -plumboles, dianionic aromatic compounds containing tin and lead atoms in their π-skeletons, opened a new field of transition-metal chemistry. Since the discovery of ferrocene (CpFe), which is composed of anionic aromatic ligands (Cp: cyclopentadienyl) and Fe(II), ferrocene-type sandwich complexes have long played important roles in many fields of chemistry. During the last few decades, the electronic and structural properties of the Cp ligand have been modified by introducing electron-donating, electron-withdrawing, and sterically encumbered substituents on the skeletal carbon atoms to obtain desirable properties of the resulting sandwich complexes.

Relativistic Effect on J(M,C) in Me M, Me M , Ph M, and Ph M (M=Pb, Sn, Ge, Si, and/or C): Role of s-Type Lone Pair Orbitals in the Distinct Effect for the Anionic Species.

Indirect one-bond nuclear spin-spin couplings between M and C [ J(M,C)] in Me M, Me M , Ph M, and Ph M (M=Pb, Sn, Ge, Si, C) are analyzed with consideration of the relativistic effect and by employing Slater-type basis sets. The evaluated total values J (M,C) reproduced the observed values with some systematic calculation errors. Fermi contact terms J (M,C) contribute predominantly to J (M,C) (≈99 %).

Reactions of Dilithium Dibenzopentalenides with Cr(CO) (CH CN) : Unexpected Formation of a Cubic Tetramer of an Anionic Hydrodibenzopentalenyl Complex.

To explore the coordination chemistry of dibenzopentalene dianion, reactions of two dilithium dibenzopentalenides having different silyl substituents with Cr(CO) (CH CN) were investigated. The products were unexpected anionic complexes, [Li(Et O)] [Cr(η -9-hydrodibenzopentalenyl)(CO) ] . The proton at the 9-position is derived from Cr(CO) (CH CN) , as evidenced by the use of Cr(CO) (CD CN) .

Synthesis and reactivity of a ruthenocene-type complex bearing an aromatic π-ligand with the heaviest group 14 element.

An anionic ruthenocene derived from a dilithioplumbole complex was prepared. In the complex, the plumbole ligand coordinates a ruthenium atom in an η-fashion, similar to the cyclopentadienyl ligand in ferrocene. The ruthenocene that has the aromatic π-ligand with the heaviest group 14 element reacted with electrophiles to afford the plumbole complexes wherein the plumbole ligands show deviation from planarity, in contrast to the planar plumbole ring in the anionic ruthenocene.

Triphosphasumanene Trisulfide: High Out-of-Plane Anisotropy and Janus-Type π-Surfaces.

A triphosphasumanene trisulfide was designed and synthesized as an out-of-plane anisotropic π-conjugated molecule. Incorporating three anisotropic phosphine sulfide moieties into a sumanene skeleton induced a cumulative anisotropy with a large dipole moment (12.0 D), which is aligned in perpendicular direction with respect to the π-framework and more than twice as large as those of conventional out-of-plane anisotropic molecules.

Efficient Synthesis of 1,4-Bis-heteroatom-substituted Tetraselanylbenzenes via 1,4-Dilithiation of Hexaselanylbenzene and Investigation on Their Electronic Properties.

We successfully synthesized mono- and bis-substituted polyselanylbenzenes 3 and 5 via mono- and dilithiation of hexakis(phenylselanyl)benzene (1), respectively. Introduction of various heteroatom functionalities into hexaselanylbenzene changed the electronic properties dependent on the σ-symmetric circular orbitals that were formed by the interactions between neighboring heteroatoms. In the cyclic voltammetry and theoretical studies on bis-heteroatom-substituted benzenes 5, the extent of the interactions in the circular orbitals with σ-symmetry affected the stability of the cationic species of 5.

(η(4)-Butadiene)Sn(0) Complexes: A New Approach for Zero-Valent p-Block Elements Utilizing a Butadiene as a 4π-Electron Donor.

Research on zero-valent p-block elements is a recent hot topic in synthetic and theoretical chemistry because of their novel electronic states having two lone pairs in both the s- and p-orbitals. It is considered that σ-donating ligands bearing large substituents are essential to stabilize these species. Herein, we propose a new approach using butadiene as a 4π-electron donor to stabilize zero-valent group 14 elements.

The Chemistry of Heterasumanenes.

Our studies on the synthesis of heterasumanenes, where benzylic carbon atoms of the sumanene are replaced by heteroatom functionalities, are summarized. Starting from triphenylene, repetitive lithiation at a bay position followed by introduction of silylene or germylene units provided the first trisila- and trigermasumanenes with no substituents on the skeletal carbon atoms. The synthesis of a trisilasumanene bearing six butoxy groups on the skeletal carbon atoms was also accomplished by our original sila-Friedel-Crafts reaction.

A reversible two-electron redox system involving a divalent lead species.

Reduction of THF-stabilized plumbacyclopentadienylidene with lithium afforded dilithioplumbole. On the other hand, oxidation of the dilithioplumbole provided the starting plumbacyclopentadienylidene. This is the unprecedented example of a reversible interconversion between group 14 M(II) and its dianionic species bearing organic substituents.

Synthesis, structures, and electronic properties of triple- and double-decker ruthenocenes incorporated by a group 14 metallole dianion ligand.

The neutral triple-decker ruthenocenes and anionic ruthenocene bearing a stannole dianion were successfully synthesized by the reactions of dilithiostannoles with [Cp*RuCl]4. This is the first example of a transition-metal complex bearing a group 14 metallole dianion with μ-η(5):η(5) coordination mode. These complexes were fully characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis.

Facile synthesis of dibenzopentalene dianions and their application as new π-extended ligands.

Reduction of phenyl(silyl)ethynes with potassium followed by quenching with iodine gave dibenzopentalenes in moderate yields. The intermediates of the reactions, dipotassium dibenzopentalenides, were isolated. The first dibenzopentalene-transition-metal complex was successfully synthesized.

Quantum-chemical analyses of aromaticity, UV spectra, and NMR chemical shifts in plumbacyclopentadienylidenes stabilized by Lewis bases.

We carried out a series of zeroth-order regular approximation (ZORA)-density functional theory (DFT) and ZORA-time-dependent (TD)-DFT calculations for molecular geometries, NMR chemical shifts, nucleus-independent chemical shifts (NICS), and electronic transition energies of plumbacyclopentadienylidenes stabilized by several Lewis bases, (Ph)2 ((t) BuMe2 Si)2 C4 PbL1 L2 (L1, L2 = tetrahydrofuran, Pyridine, N-heterocyclic carbene), and their model molecules. We mainly discussed the Lewis-base effect on the aromaticity of these complexes. The NICS was used to examine the aromaticity.

σ-Aromaticity in hexa-group 16 atom-substituted benzene dications: a theoretical study.

C6I6(2+) has been reported to have a σ-aromatic character since removal of two σ anti-bonding electrons localized on iodines results in fulfilling Hückel (4n+2) rules for I6(2+) as well as C6 parts. To search for molecules possessing similar character, hexa-group 16 atom-substituted benzene dications C6(ChH)6(2+) (Ch = S, Se, Te) and their derivatives are examined for aromatic character by using nucleus-independent chemical shift (NICS). For these dications, in which iodines in C6I6(2+) are replaced by group 16 atoms, negative NICS values larger in magnitude than for benzene are found when a σ anti-bonding orbital localized on group 16 atoms is unoccupied.

Diversity of the structures in a distannene complex and its reduction to generate a six-membered Ti(2)Sn(4) ring complex.

In contrast to olefin complexes, their congeners of heavier elements display various coordination modes, and their complexes may be present as bis(metallylene) complexes, with side-on coordination, as metallacyclopropanes, or as π complexes. In the course of our studies on the reactivity of dilithiostannoles towards transition-metal reagents, three-membered TiSn2 and six-membered Ti2 Sn4 ring complexes were obtained. According to its geometric parameters, NMR analysis, and theoretical calculations, the TiSn2 complex cannot be categorized into any of these previously described bonding modes.

Synthesis, structure, and reactivity of Lewis base stabilized plumbacyclopentadienylidenes.

Plumbacyclopentadienylidenes, in which the lead atoms have divalent states and are coordinated by THF, pyridine and N-heterocyclic carbene, were synthesized and characterized. The THF- and pyridine-stabilized compounds can be regarded as rare examples of hypervalent 10-X-4 species. The equilibrium between the THF adduct and the free plumbacyclopentadienylidene was evidenced by spectroscopic analysis and theoretical calculations.

Unexpected formation of Ru2Sn2 bicyclic four-membered ring complexes with butterfly and inverse-sandwich structures.

Reactions of tetraethyldilithiostannole 1 with [Cp*RuCl]4 afforded not η(5)-stannole dianion complexes but two novel bis(stannylene)-bridged dinuclear ruthenium complexes, which have butterfly and inverse-sandwich structures, respectively, depending on the stoichiometry of [Cp*RuCl]4 toward dilithiostannole. The redox behavior between the two complexes is found to be reversible. The molecular structures were determined by X-ray diffraction analysis.

1,1'-Di-tert-butyl-2,2',3,3',4,4',5,5'-octa-ethyl-1,1'-bis-tannole.

The title compound, [Sn(2)(C(4)H(9))(2)(C(12)H(20))(2)], has two 1-stannacyclo-penta-diene skeletons related by inversion symmetry located at the mid-point of the Sn-Sn bond [2.7682 (2) Å]. Thus, the asymmetric unit comprises one half-mol-ecule.